Wi-Fi technology has its origins in a 1985 ruling by the U.S. Federal Communications Commission that released the bands of the radio spectrum at 900 megahertz (MHz), 2.4 gigahertz (GHz), and 5.8 GHz for unlicensed use by anyone. Technology firms began building wireless networks and devices to take advantage of the newly available radio spectrum, but without a common wireless standard the movement remained fragmented, as devices from different manufacturers were rarely compatible. Eventually, a committee of industry leaders came up with a common standard, called 802.11, which was approved by the Institute of Electrical and Electronics Engineers (IEEE) in 1997. Two years later a group of major companies formed the Wireless Ethernet Compatibility Alliance (WECA, now the Wi-Fi Alliance), a global nonprofit organization created to promote the new wireless standard. WECA named the new technology Wi-Fi. Subsequent IEEE standards for Wi-Fi have been introduced to allow for greater bandwidth. The original 802.11 standard allowed a maximum data transmission rate of only 2 megabits per second (Mbps); 802.11n, introduced in 2007, has a maximum rate of 600 Mbps.
Under the IEEE Wi-Fi standards, the available frequency bands are split into several separate channels. These channels overlap in frequency, and therefore Wi-Fi uses channels that are far apart. Within each of these channels, Wi-Fi uses a “spread spectrum” technique in which a signal is broken into pieces and transmitted over multiple frequencies. Spread spectrum enables the signal to be transmitted at a lower power per frequency and also allows multiple devices to use the same Wi-Fi transmitter. Because Wi-Fi signals are often transmitted over short distances (usually less than 100 metres [330 feet]) in indoor environments, the signal can reflect off walls, furniture, and other obstacles, thus arriving at multiple time intervals and causing a problem called multipath interference. Wi-Fi reduces multipath interference by combining three different ways of transmitting the signal (in a method developed by Australian engineer John O’Sullivan and collaborators). The popularity of Wi-Fi has grown steadily. Wi-Fi allows local area networks (LANs) to operate without cables and wiring, making it a popular choice for home and business networks. Wi-Fi can also be used to provide wireless broadband Internet access for many modern devices, such as laptops, smartphones, tablet computers, and electronic gaming consoles. Wi-Fi-enabled devices are able to connect to the Internet when they are near areas that have Wi-Fi access, called “hot spots.” Hot spots have become common, with many public places such as airports, hotels, bookstores, and coffee shops offering Wi-Fi access. Some cities have constructed free citywide Wi-Fi networks. A version of Wi-Fi called Wi-Fi Direct allows connectivity between devices without a LAN. Radiotelegraphy, radio communication by means of Morse Code or other coded signals. The radio carrier is modulated by changing its amplitude, frequency, or phase in accordance with the Morse dot-dash system or some other code. At the receiver the coded modulation is recovered by an appropriate demodulator and the code groups are converted into the corresponding symbols. In many instances the symbols are generated by a computer and modem rather than with a manual telegraph key.
C. Liquid molecules and atoms are able to slip around each other and fill in gaps between them.
Explanation:
The liquid is a state of matter that has no definite shape. In fact, it can adapt to the shape of its container. This is because of the reason that molecules in the liquid phase have high kinetic energy and weak binding forces. The high energy keeps them moving freely and thus can take the shape of it its container. On the other hand, in solids, the binding forces are stronger and molecules have very little energy to move freely.
Example: If we melt a solid, the molecules initially have less energy. However, when we heat them, they gain energy and start moving. Upon further heating, they will have enough energy to break the bondings and move around. This is why the solid structure will change to the liquid.
The Rhizaria are supergroup species of mostly unicellular eukaryotes and classified as protista. Rhizaria include species like cercozoa, foraminifera and radiolaria.
<u>Some of the attributes of Rhizaria are:</u>
non-photosynthethic in nature, but some have a symbiotic relationship with unicellular algae.
express only rDNA sequences so they can vary in different forms.
do not have clear morphological characters
they mostly includes amoebas which functions for food engulfing and help to direct movement in rhizarian protista.
<u>Contribution of Rhizaria to the ecosystem:</u>
There are known as abundant bacterial grazers, and play very important role in microbial food webs.
They provide a wide diversity of marine organisms.
